System and method for sensing load on a downhole tool

ABSTRACT

A system and method for determining load on a downhole tool according to which one or more sensors are embedded in one or more components of the tool or in a material on one or more of the components. The sensors are adapted to sense load on the components.

BACKGROUND

This disclosure relates to a system and method for determining loadtransmitted to a downhole tool in oil and gas recovery operations.

Many downhole tools are subjected to loads during oil and gas recoveryoperations. For example, packers are used to seal against the flow offluid to isolate one or more sections, or formations, of a wellbore andto assist in displacing various fluids into the formation and/orretrieving hydrocarbons from the formation. The packers are suspended inthe wellbore, or in a casing in the wellbore, from a work string, or thelike, consisting of a plurality of connected tubulars or coiled tubing.Each packer includes one or more elastomer elements, also known aspacker elements, which are activated, or set, so that they are forcedagainst the inner surface of the wellbore, or casing, and compressed toseal against the flow of fluid and therefore to isolate certain zones inthe well. Also, mechanical slips are located above and/or below thepacker elements and, when activated, are adapted to extend outwardly toengage, or grip, the casing or wellbore.

The packer is usually set at the desired depth in the wellbore bypicking up on the work string at the surface, rotating the work string,and then lowering the work string until an indicator at the surfaceindicates that some of the slips, usually the ones located below thepacker elements, have extended outwardly to engage the casing orwellbore. As additional work string weight is set down on the engagedslips, the packer elements expand and seal off against the casing orwellbore. Alternately, the packer can be set by establishing a hydraulicpressure into a setting mechanism by the work string. The settingmechanism then extends, sets the packer, and expands all slips to engagethe casing or wellbore.

Usually, the setting and sealing is accomplished due to the fact thatthe packer elements are kept sealed against the casing or wellbore bythe weight, or load, of the work string acting against the slips. It canbe appreciated that it would be advantageous to be able to monitor,evaluate, and, if necessary, vary, the load transmitted to the packerand other downhole packers. Although a weight indicator has beenprovided at the surface for this purpose, it is often difficult todetermine exactly how much load is being transmitted due, for example,to buckling and corkscrewing of the work string, irregular wellborediameters, etc.

Therefore, what is needed is a system and method for sensing andmonitoring the load transmitted to a downhole packer in the above mannerso that the load can be evaluated and, if necessary, adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional/partial elevational view of a downhole oiland gas recovery operation utilizing a tool according to an embodimentof the invention.

FIG. 2 is a cross-sectional view of the tool of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, the reference numeral 10 refers to a wellborepenetrating a subterranean formation F for the purpose of recoveringhydrocarbon fluids from the formation F. A tool 12, in the form of apacker, is located at a predetermined depth in the wellbore 10, and awork string 14, in the form of jointed tubing, coiled tubing, wireline,or the like, is connected to an upper end of the packer 12. The tool 12is shown generally in FIG. 1 and will be described in detail later.

The work string 14 extends from a rig 16 located above ground andextending over the wellbore 10. The rig 16 is conventional and, as such,includes support structure, draw works, a motor driven winch, and/orother associated equipment for receiving and supporting the work string14 and the tool 12 and lowering the packer 12 to the predetermined depthin the wellbore 10.

The wellbore 10 can be lined with a casing 18 which is cemented in thewellbore 10 by introducing cement in an annulus formed between an innersurface of the wellbore 10 and an outer surface of the casing 18, all ina conventional manner.

The tool 12 is shown in detail in FIG. 2 and includes a mandrel 20formed by two telescoping mandrel sections 20 a and 20 b, with an upperend portion of the mandrel section 20 b, as viewed in FIG. 2, extendingover a lower end portion of the mandrel section 20 a. An upper end ofthe mandrel section 20 a is connected to the work string 14 (FIG. 1).

Packer element 22 comprises two axially-spaced annular packer elements22 a and 22 b extending around the mandrel section 20 a and between ashoulder formed on the mandrel section 20 a and the corresponding end ofthe mandrel section 22 b. The packer elements 22 a and 22 b are adaptedto be set, or activated, in the manner discussed above which causes themto extend radially outwardly to the position shown in FIG. 2 to engagethe inner surface of the casing 18 and seal against the flow of fluidsto permit the isolation of certain zones in the well.

The packer element 22 b is spaced axially from the packer element 22 a,and a spacer ring 24 extends around the mandrel section 20 a and betweenthe packer elements 22 a and 22 b. A shoe 26 a extends around themandrel section 20 a just above an upper end of the packer element 22 a,and a shoe 26 b extends around the mandrel section 20 a just below alower end of the packer element 22 b.

A plurality of mechanical slip elements 28, two of which are shown inFIG. 2, are angularly spaced around the mandrel section 22 b with aportion of each extending in a groove formed in the outer surface of themandrel section 22 b. The slip elements 28 are adapted to be set, oractivated, in the manner discussed above to cause them to extendradially outwardly to the position shown in FIG. 2 to engage, or grip,the inner surface of the casing 18 to hold the tool 12 in apredetermined axial position in the wellbore 10.

Three axially-spaced sensors 30 a, 30 b, and 30 c are located on themandrel 20, and a sensor 30 d is located on each slip element 28. Threeadditional sensors 30 e, 30 f, and 30 g are located on the spacer ring24, the shoe 26 a, and the shoe 26 b, respectively.

Before the sensors 30 a-30 g are applied to the tool 12 in the abovelocations, they are embedded in a non-metallic material and the materialis applied to the tool. For example, the sensors 30 a-30 g can beembedded in a laminated structure including multiple sheets of materialthat are laminated together. Each sheet is formed of a compositematerial including a matrix material, such as a polymer and a braidimpregnated in the matrix material. The braid could be in the form of asingle strand or multiple strands woven in a fabric form. The sensors 30a-30 g, along with the necessary electrical conductors, are placedeither in the matrix material or within the braided strands of thebraid. The sheets are adhered together with an adhesive, a plasticmaterial, or the like, to form the laminated structure. Alternately thesensors 30 a-30 g could be located between adjacent sheets in the abovelaminated structure.

The laminated structure thus formed, including the sensors 30 a-30 g,can be attached to an appropriate surface of the mandrel 20, the slipelements 28, the spacer ring 24, and/or the shoes 26 a and 26 b in anyconventional manner, such as by adhesive, or the like, or they can beplaced loosely against an appropriate structure.

The above-mentioned electrical conductors associated with the sensors 30a-30 g are connected to appropriate apparatus for transmitting theoutput signals from the sensors 30 a-30 g to the ground surface. Forexample, each sensor 30 a-30 g can be hardwired to centralstorage/calibration electronics (not shown) at the ground surface usingelectrical conductors or fiber optics. Alternately, data from thesensors 30 a-30 g can be transmitted to central storage/calibrationelectronics at the ground surface via high-frequency, radio frequency,electromagnets, or acoustic telemetry. Also, it is understood that eachsensor 30 a-30 g can be set up to store data independently from theother sensors and the stored data can be accessed when the tool 12 isreturned to the ground surface.

Alternately, one or more of the mandrel 20, the spacer ring 24, and/orthe shoes 26 a and 26 b can be fabricated from the above laminatedstructure including the sensors 30 a-30 g and the appropriate electricalconductors. A technique of incorporating sensors in structure notrelated to downhole tools is disclosed in a paper entitled “IntegratedSensing in Structural Composites” presented by A. Starr, S.Nemat-Nasser, D. R. Smith, and T. A. Plaisted at the 4^(th) AnnualInternational Workshop for Structural Health Monitoring at StanfordUniversity on Sep. 15, 2003, the disclosure of which is incorporatedherein by reference in its entirety.

In each of the above cases, all loads transmitted to the mandrel 20, theslip elements 28, the spacer ring 24, and/or the shoes 26 a and 26 b aresensed by the sensors 30 a-30 g.

The sensors 30 a-30 g can be in the form of conventional strain gaugeswhich are adapted to sense the stress in the mandrel 20, the packerelement 22, the slip elements 28, the spacer ring 24, and the shoes 26 aand 26 b and generate a corresponding output signal. An example of thistype of sensor is marketed under the name Weight-on-Bit (WOB)/TorqueSensor, by AnTech in Exeter, England and is disclosed on Antech'sInternet website at the following URL address:http://www.antech.co.uk/index.html, and the disclosure is incorporatedherein by reference in its entirety.

The sensors 30 a-30 g can be connected in a conventional Wheatstonebridge with the measurements of strain (elongation) by the sensors 30a-30 g being indicative of stress level. As a result, the load on themandrel 20, the packer element 22, the slip elements 28, the spacer ring24, and the shoes 26 a and 22 b can be calculated as follows:L=S(A)

where:

-   -   L is the applied load on the mandrel 20, the packer element 22,        the slip elements 28, the spacer ring 24, and the shoes 26 a and        26 b;    -   S is the stress which equals the measured strain times the        modulus of elasticity which is a constant for the material of        the mandrel 20, the slip elements 28, the spacer ring 24, and        the shoes 26 a and 26 b; and    -   A is the cross-section area of the mandrel 20, the slip elements        28, the spacer ring 24, and the shoes 26 a and 26 b.

It is understood that, additional electronics, such as a power supply, adata storage mechanism, and the like, can be located anywhere on thetool 12 and can be associated with the sensors 30 a-30 g to enable andassist the sensors 30 a-30 g to function in the above manner. Sincethese electronics are conventional they are not shown nor will they bedescribed in detail.

The sensors 30 a-30 g can be set up to store data independently from theother sensors, or can be “hardwired” to central storage/calibrationelectronics (not shown) using electrical conductors (wire) or fiberoptics, or can be connected locally to central storage/calibrationelectronics via high-frequency, radio/frequency, electromagnetic, oracoustic telemetry.

The readings from all the sensors 30 a-30 g can be used individually orcan be combined to form a “virtual” sensor anywhere on the tool 12. Inother words, the readings from all or a portion of the sensors 30 a-30 gcan be used to estimate the stress/strain, etc. at any point on the tool12 including actual sensor locations. Even though one of the sensors 30a-30 g may be present at a location of interest on the tool 12, theaccuracy of the measurement may be improved by also using the othersensor measurements as well. Also, a calibration can be performed on theentire tool 12 under various loading conditions, in a manner so that itwould not be necessary to precisely align or attach the sensors 30 a-30g in a particular way, since the calibration would compensate for sensormisalignment, etc.

Variations

1. The number of sensors 30 a-30 g that are used on the tool 12 can bevaried.

2. The sensors 30 a-30 g can be located anywhere on the mandrel 20, theslip elements 28, the spacer ring 24, and the shoes 26 a and 26 b,preferably in areas subjected to relatively high strain, and could alsobe located on one or more of the packer elements 22 a and 22 b.

3. The location of the sensors 30 a-30 g is not limited to the mandrel20, the slip elements 28, the spacer ring 24, and the shoes 26 a and 26b, but could be at any area(s) of the tool 12.

4. The sensors 30 a-30 g are not limited to strain gauges but rather canbe in the form of any type of sensors that sense load.

5. The material in which the sensors 30 a-30 g are embedded can vary.For example the material can be an elastomer, ceramic, plastic, glass,foam, or wood with or without the above-mentioned braid integratedtherein. Also, the material does not necessarily have to be in the formof sheets or laminated sheets.

6. Although the tool 12 is shown in a substantial vertical alignment inthe wellbore 10, it is understood that the packer 12 and the wellbore 10can extend at an angle to the vertical.

7. The present invention is not limited to sensing loads on packers butrather is applicable to any downhole tool.

8. The spatial references mentioned above, such as “upper”, “lower”,“under”, “over”, “between”, “outer”, “inner”, and “surrounding” are forthe purpose of illustration only and do not limit the specificorientation or location of the components described above.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. An assembly for sensing load on a downhole tool, comprising: anon-metallic material attached to the tool; and at least one sensorembedded in the material.
 2. The assembly of claim 1 wherein thematerial comprises a matrix material.
 3. The assembly of claim 1 whereinthe material comprises a braid.
 4. The assembly of claim 3 wherein thebraid comprises a single strand or multiple strands woven in a fabricform.
 5. The assembly of claim 1 wherein the material comprises a matrixmaterial and a braid embedded in the matrix material, and wherein thesensor is embedded in the braid.
 6. The assembly of claim 5 wherein thematrix material and the braid are formed into sheets, and wherein thesheets are laminated together.
 7. The assembly of claim 1 wherein thematerial comprises a plurality of laminated sheets, and wherein thesensor is located between two adjacent sheets.
 8. The assembly of claim1 further comprising electrical conductors connected to the sensor andembedded in the material.
 9. The assembly of claim 1 wherein the toolcomprises at least one sealing element adapted to sealingly engage awellbore, and wherein the material is located adjacent the sealingelement.
 10. The assembly of claim 1 wherein the tool comprises at leastone slip element adapted to grip an inner surface of a wellbore, andwherein the material is attached to the slip element.
 11. A downholetool comprising: a plurality of elements at least one of which isfabricated from a non-metallic material; and at least one sensorembedded in the material.
 12. The tool of claim 11 wherein the materialcomprises a matrix material.
 13. The tool of claim 11 wherein thematerial comprises a braid.
 14. The tool of claim 13 wherein the braidcomprises a single strand or multiple strands woven in a fabric form.15. The tool of claim 11 wherein the material comprises a matrixmaterial and a braid embedded in the matrix material, and wherein thesensor is embedded in the braid.
 16. The tool of claim 15 wherein thematrix material and the braid are formed into sheets, and wherein thesheets are laminated together.
 17. The tool of claim 11 wherein thematerial comprises a plurality of laminated sheets, and wherein thesensor is located between two adjacent sheets.
 18. The tool of claim 11further comprising electrical conductors connected to the sensor andlocated in the material.
 19. The tool of claim 11 wherein one of theelements is a sealing element adapted to sealingly engage a wellbore,and wherein another element is a shoe associated with the sealingelement and fabricated from the material.
 20. The tool of claim 11wherein two of the elements are sealing elements adapted to sealinglyengage a wellbore, and wherein another element is a spacer ringextending between the sealing elements and fabricated from the material.21. The tool of claim 11 wherein one of the elements is a mandrelfabricated from the material.
 22. A method of sensing load on a downholetool, comprising the steps of: embedding a load sensor in a non-metallicmaterial; and attaching the material to the tool.
 23. The method ofclaim 22 wherein the material comprises a matrix material.
 24. Themethod of claim 22 wherein the material comprises a braid.
 25. Themethod of claim 24 wherein the braid comprises a single strand ormultiple strands woven in a fabric form.
 26. The method of claim 22wherein the material comprises a matrix material, and further comprisingthe steps of: embedding the sensor in a braid; and embedding the braidin the matrix material.
 27. The method of claim 22 further comprisingthe steps of: connecting electrical conductors to the sensor; andembedding the electrical conductors in the material.
 28. The method ofclaim 22 wherein the material comprises a plurality of laminated sheets,and wherein the sensor is located between two adjacent sheets.
 29. Themethod of claim 22 wherein the tool is a packer having a sealing elementadapted to sealingly engage a wellbore, and further comprising the stepof disposing the sensor adjacent the sealing element.
 30. The method ofclaim 22 wherein the tool is a packer having at least one slip elementadapted to grip an inner surface of a wellbore, and wherein the materialis attached to the slip element.
 31. A method of sensing a load on adownhole tool, comprising the steps of: fabricating at least a portionof the tool of a non-metallic material; and embedding at least one loadsensor in the material.
 32. The method of claim 31 wherein the materialcomprises a matrix material.
 33. The method of claim 31 wherein thematerial comprises a braid.
 34. The method of claim 33 wherein the braidcomprises a single strand or multiple strands woven in a fabric form.35. The method of claim 31 wherein the material comprises a matrixmaterial, and further comprising the steps of: embedding the sensor in abraid; and embedding the braid in the matrix material.
 36. The method ofclaim 31 wherein the material comprises a laminated structure having aplurality of the sheets laminated together, and further comprising thestep of disposing the sensor between two adjacent sheets.
 37. The methodof claim 31 wherein the tool is a packer, and further comprising thestep of fabricating a portion of the packer with the material.
 38. Themethod of claim 31 further comprising the steps of: connectingelectrical conductors to the sensor; and embedding the electricalconductors in the material.
 39. The method of claim 31 wherein eachsensor is adapted to sense stress on that part of the tool where thesensor is located.
 40. The method of claim 39 wherein a plurality ofsensors are embedded in the material and are adapted to store datarelating to the sensed stress independently from the other sensors. 41.The method of claim 39 wherein a plurality of sensors are embedded inthe material, and further comprising the step of connecting the sensorsto central storage/calibration electronics which receives the sensedstress data from all of the sensors.
 42. The method of claim 41 whereinthe sensors are hardwired to the electronics.
 43. The method of claim 41wherein the sensors are connected to the electronics via high frequency,radio frequency, electromagnetic, or acoustic telemetry.
 44. The methodof claim 41 wherein the electronics combine the outputs of the sensorsto form a virtual sensor anywhere on the tool.
 45. The method of claim44 further comprising the step of utilizing the electronics to estimatethe stress at any point on the tool including the actual sensorlocations.
 46. The method of claim 41 further comprising the step ofutilizing the electronics to calibrate the sensors to compensate forsensor misalignment.